Funds are requested to purchase a Bruker ELEXSYS 580 pulse spectrometer capable of running double electron electron resonance (DEER), double quantum coherence (DQC), and electron nuclear double resonance (ENDOR) experiments at cryogenic temperatures. Pulse instrumentation of this kind is not available at the Medical College of Wisconsin (MCW), or in the surrounding regional community. Recent advances in the commercial instrumentation and application of pulsed EPR spectroscopy are rapidly making this technique essential to the site-directed spin labeling (SDSL) and metal EPR research communities. The ability of DEER and DQC methods to measure interspin distances in the range of 15-50[unreadable] opens up an entirely new range of possibilities in the study of biomedically significant research problems. [unreadable] [unreadable] Five major users will utilize this instrument to measure long distance ranges within protein or peptide systems. In addition, numerous minor users are identified, each with a need for advanced pulse instrumentation not available in the region. Each major user is NIH-funded and has an established and growing research group dedicated to the advancement of protein structure and functional dynamics. This instrumentation will immediately and significantly advance the productivity of the projects outlined in this proposal in addition to enhancing the research environment for the surrounding community. [unreadable] [unreadable] Having the pulse capability that this instrumentation will provide is vital to the rapid progress of the discussed NIH-funded projects as well as to providing MCW researchers and visitors access to state-of-the-art EPR instrumentation. [unreadable] [unreadable] [unreadable]